GORUCK GR1 Sizing Chart
The Special Forces curse clearly states, the more space you have, the more stuff you’ll pack. But, sometimes you need more stuff, and fit matters. The 21L GR1® is 18" tall and the 26L GR1® is 20" tall. The classic 21L GR1® fits all shapes and sizes. If you’re ~6’+ and/or want 5 additional liters and 2” of additional height, go with the Larger 26L. When moving through airports, commuting, or rucking, the goal is for your ruck to be high on your back. No matter how tall you are, the 21L will rest 2” higher than the 26L.
If you're the kind of person who prides yourself in minimalist packing, go with the 21L. If you like more space and always carry more stuff, go with the 26L.